The present invention relates to a good machinability Fe-based sintered alloy and a process of manufacture therefor, and more particularly relates to a technique which can improve machinability by sintering a boron compound powder added to a mixed powder of an Fe-based material.
An Fe-based sintered alloy can be produced in near-net shape so that manufacturing cost for processing can be reduced, and moreover, elements may be dispersed therein having specific gravities which differ greatly, and in different alloys in which dissolution is difficult, whereby properties may be obtained such as wear resistance, etc. For this reason, Fe-based sintered alloys are often used in various fields of technology. For example, mechanical parts made of Fe-based sintered alloy can be made without considerable machining processing, even if the parts are of complicated configuration, whereby such parts can be widely employed in valve driving systems, bearings, and the like, in automobiles, motorcycles, etc. However, most mechanical parts made of Fe-based sintered alloys must be machined, therefore poor machinability still present problems.
In order to improve the machinability of Fe-based sintered alloys, many attempts have heretofore been made. In one attempt, an Fe powder containing sulfur is used as a starting material powder. In another attempt, sulfide is added to and mixed with a starting material powder. In still another attempt, a sintered compact is sulfurized in an atmosphere of hydrogen sulfide gas. However, when sulfur as a cutting facilitating component is dispersed in the matrix of a sintered alloy, improvement in machinability is limited. Moreover, sulfur is an element which decreases strength, particularly toughness, in sintered alloys, and also promotes corrosion in sintered alloys; therefore, use of such sintered alloys is limited.
Another technique which fills resin, etc., into pores of a sintered alloy is also available. In such a sintered alloy, the resin in the pore serves as an initiating point for chip breaking, whereby the chip-breaking property is superior. However, in such a technique, using certain types of resin may shorten the service life of a cutting tool such as a cutter. Moreover, a process for removing the resin from the pores after cutting processing may be required, depending on the purpose for which the sintered alloy is to be used.
Therefore, the present applicant proposed an improved method for an Fe-based sintered alloy, in which a boron compound powder is added to a mixed powder of an Fe-based material including carbon, and is sintered, in Japanese Unexamined Patent Application Publication No. 241701/97. According to this proposed technique, diffusion of the carbon into the matrix is suppressed by the boron, whereby machinability can be improved with a decrease in hardness of the Fe-based sintered alloy.
However, further improvement of machinability has been recently demanded to enhance high performance alloys for automobiles.